This came in via the trac account request. I don't know the sender's
email address ...
-- h
---------- Forwarded message ----------
From: 'Jamel Dammak' via sage-trac-account <sage-trac-acco...@googlegroups.com>
Date: Sun, Dec 11, 2016 at 10:01 PM
Subject: [sage-trac-account] Corrections about the function "is_prime"
for graphs
To: "sage-trac-acco...@googlegroups.com" <sage-trac-acco...@googlegroups.com>
Dear sir,
there is an error concerning the function "is_prime" for graphs in
Sagemath, section Graph Theory.
Here is a conter-example.
g1=Graph({0:[1,4],1:[0,2,4],2:[1,3,4],3:[2],4:[0,1,2]});g2=Graph({0:[1],1:[0,2,4],2:[1,3,4],3:[2,4],4:[1,2,3]})
#g1.show();g2.show();
#[1,4] is a module of g1 so g1 is not prime
g2.is_isomorphic(g1), g1.is_prime(),g2.is_prime()
This is a conter-example with two isomorphic graphs g1 and g2 on 5
vertices giving two different results
with the function "is prime".
I have an algorithm giving the list of all prime graphs on at most 8 vertices.
Best regards.
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